In the operation of oil field steam flooding operations, wet steam, i.e., steam that contains water in both the liquid and vapor state is frequently injected into oil wells. The mass ratio of vapor to the sum of vapor plus liquid mass in steam is commonly referred to the "quality" of the steam.
In order to efficiently produce an oil field it is necessary to know and control the quality of steam which is being injected into the wells. Steam quality will influence the rate at which oil is produced and the ultimate recovery of the field. As a result, the economics of a field can be greatly affected by the quality of steam being injected into the ground.
Many methods have been proposed to determine the quality of steam used in injection wells. For example, in U.S. Pat. Nos. 3,499,488; 3,596,516 and 3,550,849 a side stream of steam is removed from the main line through an orifice, the liquid is removed, and the salt concentration in the liquid is determined. When the salt concentration of the feedwater is known, a set of equations relating to the steam quality and salt concentrations are solved. This method suffers from a major limitation in that the method is applicale only for a single generator connected to a single injection well. Frequently, a single steam generator will be connected to many injection wells and the steam quality at an individual well is not the same as that of the composite stream.
Another method of determining steam quality involves the use of radioactive tracers, "ASME Steam Turbine Code Test Using Radioactive Tracers", ASME Paper No. 72-WA/PTC-1.
Other methods of determining steam quality require that elaborate equipment be installed in the field. For example, see U.S. Pat. No. 4,135,387 uses acoustic equipment to disperse the phases and then measures the uniformly dispersed phase with acoustic velocity determinations.
Still other methods utilize a dual orifice meter method (for example, see U.S. Pat. No. 4,149,403, assigned to the same assignee as the present invention). These methods are useful only when the steam quality is above 50% and the accuracy of the method is about .+-.10%.
From the above, it can be seen that an accurate, safe method of determining the quality of steam in a flowing line is needed which does not require elaborate equipment. Consequently, it is an object of this invention to provide a method and means for determining steam quality which is highly accurate. It is a further object of the invention to provide a method and means for determining steam quality in which the field equipment necessary to make these determinations is relatively simple. Another object of the invention is to provide a safe means for determining the quality of steam in a flowing line. Another object of the invention is to provide a method and means in which steam quality can be measured in many wells served by a single generator. Another object of the invention is to provide a method and means in which steam quality can accurately be determined in low quality streams.